Pressure measuring catheter having reduced error from bending stresses

ABSTRACT

Bending stresses experienced by a pressure sensor mounted to a fractional flow reserve catheter when tracking the catheter through the vasculature creates a distortion of the sensor resulting in an incorrect pressure reading or bend error. In order to isolate the sensor from bending stresses, the sensor is mounted with one end coupled to the distal end of the shaft while the other end of the sensor is not coupled to the catheter so that a portion of the sensor is spaced apart from the distal end of the shaft.

RELATED APPLICATIONS

The present application claims the benefit under 35 U.S.C. §119 of U.S.Provisional Patent Application No. 62/012,628 filed on Jun. 16, 2014 andtitled FFR MICROCATHETER RIGID TIP AND CANTILEVER DESIGN.

FIELD OF THE INVENTION

The invention relates to methods and systems for determining a pressuregradient across a lesion of a vessel for calculating a Fractional FlowReserve.

BACKGROUND OF THE INVENTION

The severity of a stenosis or lesion in a blood vessel may be assessedby obtaining proximal and distal pressure measurements relative to thegiven stenosis and using those measurements for calculating a value ofthe Fractional Flow Reserve (FFR). FFR is defined as the ratio of afirst pressure measurement (P_(d)) taken on the distal side of thelesion and to a second pressure measurement taken on the proximal sideof the lesion usually within the aorta (P_(a)). Conventionally, a sensoris placed on the distal portion of a guidewire or FFR wire to obtain thefirst pressure measurement P_(d), while an external pressure transduceris fluidly connected via tubing to a guide catheter for obtaining thesecond or aortic (AO) pressure measurement P_(a). Calculation of the FFRvalue provides a lesion specific index of the functional severity of thestenosis in order to determine whether the blockage limits blood flowwithin the vessel to an extent that treatment is needed. An optimal ornormal value of FFR in a healthy vessel is 1.00, while values less thanabout 0.80 are generally deemed significant and in need of aninterventional treatment. Common interventional treatment optionsinclude balloon angioplasty and/or stent implantation.

If an interventional treatment is required, the interventional device,such as a balloon catheter, is tracked over a guide wire to the site ofthe lesion. Conventional FFR wires generally are not desired byclinicians to be used as guide wires for such interventional devices.Accordingly, if an intervention treatment is required, the cliniciangenerally removes the FFR wire, inserts a conventional guide wire, andtracks the interventional device to the treatment site over theconventional guide wire.

The mounting of a pressure sensor on the distal end of a catheter, suchas a microcatheter makes it difficult to isolate the pressure sensorfrom bending stresses experienced as a result of interaction between thepressure sensor and the housing of the catheter. Due to the highsensitivity and size of the pressure sensor used in this application,any stress placed on the pressure sensor can cause a distortion of thesensor resulting in an incorrect pressure reading or bend error.Accordingly, there remains a need for a microcatheter to obtain pressuremeasurements suitable for use in calculating an FFR value for a givenstenosis, whereby the clinician may use a conventional or preferentialguidewire instead of a FFR guidewire. In addition, there remains a needfor a FFR microcatheter to reduce the amount of bending stressesexperienced by the pressure sensor in order to minimize bending error inthe pressure reading.

BRIEF SUMMARY OF THE INVENTION

Embodiments hereof relate to a catheter, such as a pressure measurementcatheter, including an elongate shaft having a proximal end optionallycoupled to a handle or luer fitting and a distal end having a distalopening. The elongate shaft further includes a proximal portion, anintermediate portion, and a distal portion having a distal tip. In theproximal portion of the elongated shaft, a shaft wall may define twoseparate lumens: a guide wire lumen and a second or pressure sensor wirelumen, extending parallel to each other or side-by-side along theproximal portion. The distal portion of the elongate shaft is configuredto receive a guidewire in a distal portion of guidewire lumen thereof.The pressure sensing wire lumen may extend to the distal portion of theelongate shaft to be coupled to a pressure sensor disposed in a pocketof the distal tip for measuring a pressure of a fluid within lumen ofvessel. Pressure sensor may be mounted on top of an interposer such thatthe sensor is elevated above the shaft wall and spaced apart from thesidewalls of the pocket, thereby isolating the pressure sensor from thebending stresses of the catheter.

Embodiments hereof also relate to a catheter, such as a measurementcatheter, including an elongate shaft having a proximal end optionallycoupled to a handle or luer fitting and a distal end having a distalopening. The elongate shaft further includes a proximal portion, anintermediate portion, and a distal portion having a distal tip. In theproximal portion of elongated shaft, shaft wall may define two separatelumens: a guide wire lumen and a second or pressure sensor wire lumen,extending parallel to each other or side-by-side along the proximalportion. The distal portion of the elongate shaft is configured toreceive a guidewire in a distal portion of the guidewire lumen thereof.The pressure sensing wire lumen may extend to the distal portion of theelongate shaft to be coupled to a pressure sensor disposed in a pocketof the distal tip for measuring a pressure of a fluid within lumen ofvessel. A step can be formed into the shaft wall under the pressuresensor such that the pressure sensor is elevated above the shaft walland spaced apart from the sidewalls of the pocket, thereby isolating thepressure sensor from the bending stresses applied to the catheter.

Embodiments hereof also relate to a catheter, such as a measurementcatheter, including an elongate shaft having a proximal end optionallycoupled to a handle or luer fitting and a distal end having a distalopening. The elongate shaft further includes a proximal portion, anintermediate portion, and a distal portion having a distal tip. In theproximal portion of elongated shaft, shaft wall may define two separatelumens: a guide wire lumen and a second or pressure sensor wire lumen,extending parallel to each other or side-by-side along the proximalportion. The distal portion of the elongate shaft is configured toreceive a guidewire in a distal portion of the guidewire lumen thereof.The pressure sensing wire lumen may extend to the distal portion of theelongate shaft to be coupled to a pressure sensor disposed in a pocketof the distal tip for measuring a pressure of a fluid within lumen ofvessel. The pressure sensor may have an elongate portion and a supportportion, whereby the support portion elevates the pressure sensor abovethe shaft wall and the pressure sensor is spaced apart from thesidewalls of the pocket in order to isolate the pressure sensor from thebending stresses applied to the catheter.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing and other features and advantages of the invention will beapparent from the following description of embodiments hereof asillustrated in the accompanying drawings. The accompanying drawings,which are incorporated herein and form a part of the specification,further serve to explain the principles of the invention and to enable aperson skilled in the pertinent art to make and use the invention. Thedrawings are not to scale.

FIG. 1 is a broken view of a system for measuring FFR with a distalportion thereof shown within a vessel including a lesion, the systemincluding a measurement catheter including a pressure sensor and aguidewire, in accordance with an embodiment hereof.

FIG. 2 is a broken view of the catheter of FIG. 1 in partiallongitudinal cross-section.

FIG. 3 is a cross-sectional view of the catheter taken along line 3-3 ofFIG. 2.

FIG. 4 is an illustration of the distal portion of the catheter of FIG.1 in longitudinal cross-section.

FIG. 4A is a perspective view of an interposer with electrical contactpads.

FIG. 4B is a perspective view of another embodiment of an interposerwith grooves formed in the electrical contact pads.

FIG. 4C is a perspective view of another embodiment of an interposerwith holes formed in the electrical contact pads.

FIG. 5 is a detailed top view of the distal portion of the catheter ofFIG. 4 including a pocket and the pressure sensor.

FIG. 6 is a perspective view of the catheter of FIG. 4 with elements ofthe catheter removed to show a more detailed view of the pressure sensorand shaft wall.

FIG. 7A is a finite element analysis representation of a sensor mountedon an elongate body showing bending induced stresses on the sensormembrane.

FIG. 7B is a finite element analysis representation of a sensorsuspended above an elongate body showing isolation of sensor membranefrom bending induced stresses.

FIG. 8 illustrates a distal portion of an embodiment of the catheter ofFIG. 1 in longitudinal cross-section.

FIG. 9 illustrates a distal portion of another embodiment of thecatheter of FIG. 1 in longitudinal cross-section.

FIG. 10 illustrates a distal portion of yet another embodiment of thecatheter of FIG. 1 in longitudinal cross-section.

DETAILED DESCRIPTION OF THE INVENTION

Specific embodiments of the present invention are now described withreference to the figures, wherein like reference numbers indicateidentical or functionally similar elements. While the disclosure refersto illustrative embodiments for particular applications, it should beunderstood that the disclosure is not limited thereto. Modifications canbe made to the embodiments described herein without departing from thescope of the present disclosure. Those skilled in the art with access tothis disclosure will recognize additional modifications, applications,and embodiments within the scope of this disclosure and additionalfields in which the disclosed examples could be applied. Therefore, thefollowing detailed description is not meant to be limiting. Further, itis understood that the systems and methods described below can beimplemented in many different embodiments of hardware. Any actualhardware described is not meant to be limiting. The operation andbehavior of the systems and methods presented are described with theunderstanding that modifications and variations of the embodiments arepossible given the level of detail presented.

References to “one embodiment,” “an embodiment,” “in certainembodiments,” etc., indicate that the embodiment described may include aparticular feature, structure, or characteristic, but every embodimentmay not necessarily include the particular feature, structure, orcharacteristic. Moreover, such phrases are not necessarily referring tothe same embodiment. Further, when a particular feature, structure, orcharacteristic is described in connection with an embodiment, it issubmitted that it is within the knowledge of one skilled in the art toaffect such feature, structure, or characteristic in connection withother embodiments whether or not explicitly described.

Specific embodiments of the present invention are now described withreference to the figures, wherein like reference numbers indicateidentical or functionally similar elements. The terms “distal” and“proximal” are used in the following description with respect to aposition or direction relative to the treating clinician. “Distal” and“distally” are positions distant from or in a direction away from theclinician. “Proximal” and “proximally” are positions near or in adirection toward the clinician.

With reference to FIG. 1, a pressure measurement catheter 10 is shownwith a proximal portion thereof outside of a patient and a distalportion thereof positioned in situ within a lumen 12 of a patient vessel14 having a stenosis or lesion 16. In an embodiment hereof, the vessel14 is a blood vessel such as but not limited to a coronary artery.Lesion 16 is generally representative of any blockage or otherstructural arrangement that results in a restriction to the flow offluid through lumen 12 of vessel 14. Lesion 16 may be a result of plaquebuildup, including without limitation plaque components such as fibrous,fibro-lipidic (fibro fatty), necrotic core, calcified (dense calcium),blood, fresh thrombus, and mature thrombus. Generally, the compositionof lesion will depend on the type of vessel being evaluated. In thatregard, it is understood that embodiments hereof are applicable tovarious types of blockage or other narrowing of a vessel that results indecreased fluid flow.

Measurement catheter 10 is shown in FIG. 2 with a distal portion thereofin longitudinal cross-section. Measurement catheter 10 includes anelongate shaft 18 having a proximal end 20 that may be coupled to ahandle or luer fitting 22 and a distal end 24 having a distal opening26. Elongate shaft 18 further includes a proximal portion 28, anintermediate portion 30, and a distal portion 32 having a distal tip 33.Although proximal portion 28, intermediate portion 30, and distalportion 32 of elongate shaft 18 have been described separately, they aredescribed in such a manner for convenience and elongate shaft 18 may beconstructed unitarily such that the portions described are part of aunitary shaft. However, different portions of elongate shaft 18 may alsobe constructed separately and joined together.

In embodiments hereof, elongate shaft 18 or component and/or segmentsthereof may be formed of polymeric materials, non-exhaustive examples ofwhich include polyethylene terephthalate (PET), polypropylene,polyethylene, polyether block amide copolymer (PEBA), polyamide,fluoropolymers, and/or combinations thereof, either laminated, blendedor co-extruded. Optionally, the catheter shaft or some portion thereofmay be formed as a composite having a reinforcement materialincorporated within a polymeric body in order to enhance strength and/orflexibility. Suitable reinforcement layers include braiding, wire meshlayers, embedded axial wires, embedded helical or circumferential wires,and the like. In one embodiment, for example, at least a proximalportion of elongate shaft 18 may be formed from a reinforced polymerictube. In other embodiments of an elongate tubular shaft or component inaccordance herewith, a proximal segment thereof may be a hypotube of amedical grade stainless steel with outer and inner tubes of a distalsegment thereof being formed from any of the polymeric materials listedabove.

As shown in FIGS. 2-3, elongate shaft 18 has a shaft wall 34 defining aguide wire lumen 35 extending therethrough. Guide wire lumen 35 extendsthrough proximal portion 28, intermediate portion 30, and distal portion32. However, instead of the over-the-wire configuration shown in FIGS.1-3, catheter 10 may have a rapid exchange configuration wherein guidewire lumen 35 extends through distal portion 32 and intermediate portion30, and the guidewire exits shaft 18 through a rapid exchange port (notshown) in proximal portion 28, as would be understood by those skilledin the art. In one embodiment, with reference to the cross-sectionalview of FIG. 3 (taken along line 3-3 of FIG. 2), in proximal portion 28of elongated shaft 18, shaft wall 34 defines two separate lumens, guidewire lumen 35 and a second or pressure sensor wire lumen 36, extendingparallel to each other or side-by-side along proximal portion 28.Communication wires 42 are omitted in FIG. 3 for clarity. Althoughdepicted as circular in cross-section, one or more lumen(s) of elongatedshaft 18 may have any suitable cross-section including for examplecircular, elliptical, rectangular or crescent-shaped. As explained inmore detail below, pressure sensing wire lumen 36 may extend to distalportion 32 of elongate shaft 18 to be coupled to a pressure sensor 38,as shown in FIGS. 4-5. In one embodiment, pressure sensor wire lumen 36may be eliminated wherein a signal from pressure sensor 38 is sent to acomputing device 40 other than via a wire 42 in a dedicated pressuresensor wire lumen 36, such as, but not limited to, wireless transmissionor integration of wire 42 into the wall of elongate shaft 18. In otherembodiments of an elongate shaft or tubular component in accordanceherewith, pressure sensor wire lumen 36 may be eliminated wherein theshaft or a portion thereof may be formed by a tubular polymeric innerliner overlaid with a power lead layer and a polymeric outer jacket. Insuch an embodiment, the power leads for the respective pressure sensorof the inner shaft may be wrapped around the respective shaft for all orat least a portion of the shaft and secured in position by the polymericouter jacket so as to be embedded within the shaft. In another suchembodiment, the power lead for the respective pressure sensor of theinner shaft may be straight for a section or for the entire length ofthe shaft, and secured in position against the inner liner by thepolymeric outer jacket so as to be embedded within the shaft.

Distal portion 32 of elongate shaft 18 is configured to receive aguidewire 44 in a distal portion of guidewire lumen 35 thereof. Further,as shown in FIG. 1, distal portion 32 is sized to extend from a proximalside 46 of lesion 16, through lesion 16, and to a distal side 48 oflesion 16 such that distal tip 33 is disposed on distal side 48 oflesion 16. Accordingly, in an embodiment, distal portion 32 has a lengthL_(D) in the range of 25-300 mm. However, length L_(D) may be any lengthsuitable such that distal portion 32 may extend from proximal side 46 todistal side 48. Further, because distal portion 32 is configured toextend through lesion 16, the cross-sectional dimension or profile ofdistal portion 32 is minimized such as to minimize the disruption ofblood flow through lesion 16 in order to obtain an accurate FFRmeasurement.

Distal tip 33 is disposed on distal portion 32 of elongate shaft 18. Inan optional embodiment (not shown), distal tip 33 is disposed onintermediate portion 30 of elongate shaft 18 and is located proximallyof distal portion 32. Distal tip 33 includes pressure sensor 38 formeasuring a pressure of a fluid within lumen 12 of vessel 14, as shownin FIGS. 4-5. In the embodiment shown in FIGS. 4-5, pressure sensor 38is disposed in a pocket 50 of a thickened portion 52 of distal tip 33.As shown in FIGS. 4-5, pocket 50 may be defined by at least onesubstantially vertical sidewall 54 and substantially horizontal shaftwall 34. In another embodiment, pocket 50 has at least one sidewall witha curvilinear shape. Pressure sensor 38 may be a piezo-resistivepressure sensor, a piezo-electric pressure sensor, a capacitive pressuresensor, an electromagnetic pressure sensor, an optical pressure sensor,and/or combinations thereof. In one non-limiting example pressure sensor38 is a micro electromechanical sensor (MEMS) based pressure diemeasuring about 240 microns by 70 microns by 1100 microns in size.However, other sized pressure sensors may be used. As shown in FIG. 2,thickened portion 52 needs to accommodate pressure sensor 38.Accordingly, thickened portion 52 of elongate shaft 18 causes tipportion 33 to have an outer diameter OD₁ (shown in FIG. 2) which islarger than the outer diameter OD₂ of distal portion 32 of elongateshaft 18. However, depending on the size of pressure sensor 38, theouter diameters OD₁ and OD₂ of the elongate shaft 18 could havesubstantially the same diameter. In one embodiment, outer diameter OD₁of tip portion 33 is in the range of 0.024 inch-0.040 inch in order toaccommodate pressure sensor 38. However, outer diameter OD₁ may varydepending on the size of pressure sensor 38, thickness of elongate shaft18, and other factors used to determine the diameter or profile ofshafts. In an optional embodiment, a cover (not shown) could extendsubstantially over pocket 50 to protect pressure sensor 38 fromcontacting the vessel wall while still allowing blood flow to surroundpressure sensor 38.

Pocket 50 is in communication with pressure sensor wire lumen 36 suchthat any communication wire(s) 42 from pressure sensor 38 may extendfrom pocket 50 proximally through pressure sensor wire lumen 36, througha corresponding lumen in luer fitting 22 exiting through proximal port54 to a computing device 40 coupled to proximal end 56 of communicationwire 42. Proximal end 56 of communication wire 42 may be coupled tocomputing device 40 via various communication pathways, including butnot limited to one or more physical connections including electrical,optical, and/or fluid connections, a wireless connection, and/orcombinations thereof. Accordingly, it is understood that additionalcomponents (e.g., cables, connectors, antennas, routers, switches, etc.)not illustrated in FIG. 1 may be included to facilitate communicationbetween the proximal end 56 of communication wire 42 and computingdevice 40. In an optional embodiment, computing device 40 isincorporated into catheter 10 or for example, in proximal portion 28.

FIG. 4 is a cross-sectional view of distal tip 33. Therein, sensor 38has a first surface 60, second surface 62, first end 64 and a second end66. Communication wires 42 (for example, 0.0025 inch coated copper wirein a tri-filar configuration) extending from lumen 36 are coupled to anelectrical interface, such as an interposer 70 which has first andsecond surfaces 72, 74. In this embodiment, communication wires form an“S-shape”, such that one end of the communication wires 42 is raised upto the elevated level of first surface 72 of interposer 70. Secondsensor surface 62 is coupled to first surface 72 of interposer 70 (forexample, by an adhesive 76), thereby disposing interposer between shaftwall 34 of elongate shaft 18 and sensor 38. FIG. 5 is a top view ofdistal tip 33 showing pocket 50 open to the environment. Thus, sensor38, wires 42, 80 and interposer 70 are in communication with a fluidwithin lumen 12 of vessel 14.

Sensor wires 80 (for example, 0.001 inch gold wires) have a first endcoupled to first surface 72 of interposer 70 and a second end coupled tofirst surface 60 of sensor 38. Similarly to the communication wires,sensor wires may also make an S-shape, such that one end of the sensorwires 80 is raised up to the elevated level of first surface 60 ofsensor 38. Because electrical contact pads 77 (as shown in FIG. 4A) onsensor 38 are extremely small (for example 0.200 mm length×0.050 mmwidth) and the metallization profile is dependent on the manufacturer,the use of an interposer optimizes the size, layout and metallization ofthe pads. In another embodiment shown in FIG. 4B, grooves 78 are formedinto interposer 70 to better facilitate the coupling (for example bywelding or soldering) of communication wires 42 or sensor wires 80 tointerposer 70. Grooves 78 form a V-shaped cross section (however othercross sectional shapes are possible) and extend from the one end ofinterposer 70 into electrical contact pads 77. Since interposer 70 andcommunication and sensor wires 42, 80 are relatively small, grooves 78help guide communication and sensor wires 42, 80 into proper placementonto first surface 72 of interposer 70. In another embodiment shown inFIG. 4C, holes 79 are formed into contact pads 77 to better facilitatethe placement and coupling (for example by welding or soldering) ofcommunication wires 42 or sensor wires 80 to interposer 70. Holes 79 arecylindrical in shape (however, other shapes are possible) and extendthrough electrical contacts pads 77 and into interposer 70.

FIG. 6 is an enlarged perspective view of sensor 38, wires 42, 80 andinterposer 70. Other portions of catheter 10 are removed to better showspecific attributes of the present Invention. Interposer 70 has secondsurface 74 coupled to shaft wall 34 of elongate shaft 18. In oneembodiment, interposer 70 is coupled to shaft wall 34 by an adhesive 82having a layer depth of about 25 microns. As described above, bendingstresses experienced when tracking a microcatheter through thevasculature may create a distortion of the sensor resulting in anincorrect pressure reading or bend error. In order to isolate sensor 38from bending stresses, sensor 38 may be mounted with first end 64 ofsensor 38 coupled to first surface 72 of interposer 70 while second end66 of sensor 38 may be suspended above shaft wall 34. Thus, second end66 of sensor 38 may not be coupled to any portion of catheter 10. Hence,sensor 38 may be cantilever mounted with proximal portion of sensor 38coupled to interposer 70. Second surface 62 of sensor 38 may be spacedapart from shaft wall 34 by having a void disposed between secondsurface 62 of sensor 38 and shaft wall 34. Sensor 38 may be elevatedabove shaft wall 34 by the thickness of interposer 70 and to some degreeby the thickness of the adhesive layers 76 and 82. Sensor 38 may beelevated above shaft wall 34 by a distance of about 40-50 microns. In anoptional embodiment, the amount of distance between the sensor 38 andshaft wall 34 is about 25-60 microns.

Second end 66 of sensor 38 may be spaced apart from sidewall 54 ofpocket 50 by having a void disposed between sensor 38 and sidewall 54 ofpocket 50. Put another way, distal portion of sensor 38 may be freefloating with respect to catheter shaft 18. Thus, as shown in FIG. 6,sensor 38 can be exposed to the environment and first surface 60, secondsurface 62 and second end 66 would be surrounded by a fluid whencatheter 10 is disposed within lumen 12 of vessel 14. In one embodiment,at least a portion of sensor 38 is suspended above shaft wall 34. Inanother embodiment, about half of sensor 38 is suspended above shaftwall 34. In yet another embodiment, more than half of sensor 38 issuspended above shaft wall 34. Thus, any length of sensor 38 can besuspended above shaft wall 34 depending on where first end 64 of sensor38 is mounted onto interposer 70.

By suspending at least a portion of sensor 38 above shaft wall 34,sensor 38 may be isolated from shaft wall 34 and further isolated fromelongate body 18 which is experiencing the bending stresses. Put anotherway, if the entire length of sensor 38 were coupled to shaft wall 34 ofelongate body 18, then sensor 38 could experience substantially the samebending stresses as shaft wall 34 of elongate body 18. FIG. 7 a showsfinite element analysis (FEA) results of Von Mises stresses 84 presentin a sensor 86 directly mounted to a shaft wall 88 of an elongate bodyof a catheter. As compared to sensor 38 with a second end 66 suspendedabove shaft wall 34 of elongate body 18 as shown in FIG. 7 b. The VonMises stresses 84 shown in FIGS. 7 a and 7 b graphically show varyingstress intensities experienced by each embodiment. As can be seen inFIG. 7 a, bending stresses extend from the shaft wall 88 of the elongatebody into the sensor 86. Whereas in FIG. 7 b, the bending stresses areisolated to just shaft wall 34, and the bending stresses do not extendinto sensor 38. By isolating the sensor 38 from bending stresses, theintegrity of sensor 38 can remain intact and the accuracy of themeasurements of sensor 38 can be improved.

FIG. 8 is an enlarged cross-sectional view of another embodiment ofdistal tip 33. In the embodiment of FIG. 8, distal tip 33 does not havean interposer or sensor wires. Instead, communication wires 42 arecoupled directly to first surface 60 of sensor 38. Sensor 38 has secondsurface 62 coupled to shaft wall 34 of elongate body 18, such as by anadhesive. In order to suspend sensor 38 above shaft wall 34, a step 90is formed or etched into shaft wall 34 to create a void between secondsurface 62 of sensor 38 and shaft wall 34. In one embodiment, distanceA, which is the measurement of step 90, measures about 40 to 50 micronsor in another embodiment about 25 to 50 microns. As previously describedwith reference to FIG. 6, second end 66 of sensor 38 may also be spacedapart from sidewall 54 of pocket 50 by having a void disposed betweensensor 38 and sidewall 54 of pocket 50. With second end 66 spaced apartfrom shaft wall 34 and sidewalls 54, at least a portion of sensor 38 maybe exposed to the environment and first and second surfaces 60, 62 couldbe surrounded by a fluid when catheter 10 is disposed within lumen 12 ofvessel 14.

FIG. 9 is an enlarged cross-sectional view of another embodiment ofdistal tip 33. In the embodiment of FIG. 9, distal tip 33 does not havean interposer, sensor wires or a step formed into shaft wall 34.Instead, sensor 38 has a support portion 92 adjacent first end 64, andan elongate portion 94. Thus, support portion 92 and elongate portion 94when taken together may form a unitary or one-piece sensor 38.Communication wires 42 are directly coupled to first surface 60 ofsensor 38. Support portion 92 of sensor 38 is coupled to shaft wall 34by, for example, an adhesive. Support portion 92 elevates elongateportion 94 above shaft wall 34 creating a void between second surface 62of sensor 38 and shaft wall 34. In the embodiment shown in FIG. 9,distance B, which is the thickness of support portion 92, measures about20 to 25 microns or in another embodiment, about 10 to 30 microns. Thus,second surface 62 of elongate portion 94 of sensor 38 is spaced apartfrom shaft wall 34 by having a void disposed between second surface 62of sensor 38 and shaft wall 34. As previously described with referenceto FIG. 6, second end 66 of sensor 38 may also be spaced apart fromsidewall 54 of pocket 50 by having a void disposed between sensor 38 andsidewall 54 of pocket 50. With second end 66 spaced apart from shaftwall 34 and sidewall 54, at least a portion of sensor 38 may be exposedto the environment and first surface 60, second surface 62 and secondend 66 could be surrounded by a fluid when catheter 10 is disposedwithin lumen 12 of vessel 14.

FIG. 10 is an enlarged cross-sectional view of another embodiment ofdistal tip 33. In the embodiment of FIG. 10, distal tip 33 does not haveinterposer, sensor wires, a step formed into shaft wall 34, and sensor38 has only an elongate portion, with no support portion as in FIG. 9.Second surface 62 of sensor 38 may be coupled to shaft wall 34 by anadhesive 92, such that the adhesive layer elevates the sensor 38 aboveshaft wall 34 creating a void between second surface 62 and shaft wall34. In one embodiment as shown in FIG. 10, distance C, which is thedistance adhesive 92 elevates sensor 38 above shaft wall 34, measuresabout 40 to 50 microns, or in another embodiment about 25-60 microns.Thus, in the embodiment of FIG. 10, the size of the void disposedbetween second surface 62 of sensor 38 and shaft wall 34 depends on thedistance C or the thickness of adhesive layer 92. As a result, secondsurface 62 of sensor 38 is spaced apart from shaft wall 34 by having avoid disposed between second surface 62 of sensor 38 and shaft wall 34.As previously described with reference to FIG. 6, second end 66 ofsensor 38 may also be spaced apart from sidewall 54 of pocket 50 byhaving a void disposed between sensor 38 and sidewall 54 of pocket 50.With second end 66 spaced apart from shaft wall 34 and sidewall 54, atleast a portion of sensor 38 may be exposed to the environment and firstsurface 60, second surfaces 62 and second end 66 could be surrounded bya fluid when catheter 10 is disposed within lumen 12 of vessel 14.

A method of measuring FFR using measurement catheter 100 will now bedescribed with reference to FIG. 1. As would be understood by thoseskilled in the art, when measuring FFR a guide catheter (not shown) maybe advanced through the vasculature such that the guide catheter isdisposed within the aorta with a distal end thereof disposed within theaorta at an ostium of the aorta adjacent the branch vessel 14 withinwhich lesion 16 is located. As shown in FIG. 1, guidewire 44 can beadvanced intraluminally through the guide catheter, into vessel 14within lumen 12 to the site of lesion 16. In the embodiment shown,guidewire 44 is advanced from proximal side 46 of lesion 16 to distalside 48 of lesion 16, which is also consistent with the direction of theblood flow BF, as indicated by the arrow BF in FIG. 1. In an embodiment,vessel 14 is a coronary artery, but vessel 14 may be other vessels inwhich it may be desirable to measure pressure, and in particular, tomeasure FFR.

Thereafter, as shown in FIG. 1, measurement catheter 10 can be trackedor advanced over indwelling guidewire 44 to the target site such thatdistal end 32 of elongate shaft 18 is positioned distal of lesion 48. Ascan be seen in FIG. 1, distal tip 33 including pressure sensor 33 can bedisposed distally of lesion 16 such that elongate shaft 18 is disposedthrough lesion 16.

With measurement catheter 10 in place, pressure sensor 33 measures thepressure of blood distal of the lesion within lumen 12. Accordingly, thepressure measured by pressure sensor 33 is the distal pressuremeasurement, or P_(d), used in calculating FFR. In one embodiment,adenosine is administered either intracoronary at the site, bolus, orintravenously by continuous infusion for providing an accurate distalpressure measurement (P_(d)) for an FFR value. A proximal pressuremeasurement P_(a), which is taken in the aorta by an external AOpressure transducer associated with the guide catheter, and asimultaneous pressure measurement P_(d) taken with pressure sensor 33 ofmeasurement catheter 10 are then obtained to provide the FFR value,i.e., P_(d)/P_(a), for the lesion. The proximal pressure measurementP_(a) and distal pressure measurement P_(d) can be communicated tocomputing device 40. Computing device 40, shown schematically in FIGS. 1and 2, may include such components as a CPU, a display device, anamplification and filtering device, an analog-to-digital converter, andvarious other components. Computing device 40 may receive the proximalpressure measurement P_(a) and distal pressure measurement P_(d), andmay process them to provide a continuous display of FFR measurement.

When the FFR measurement is completed, measurement catheter 10 may thenbe completely withdrawn from the patient or repositioned in vivo atanother lesion and the process repeated. Pressure-sensing catheters inaccordance with embodiments hereof may be used for other than providingproximal and distal pressure measurements (P_(a), P_(d)) for calculatingan FFR value. For instance, pressure-sensing catheters in accordancewith embodiments hereof may be used to provide an in vivo pressuremeasurement anywhere along the vasculature, or a particular lesiontherein. As well, embodiments hereof may be used to provide in vivopressure measurements, across a heart valve, venous valve or othervalvular location within the body where it may be deemed useful.

The detailed description is merely exemplary in nature and is notintended to limit the invention or the application and uses of theinvention. Although the description of the invention is in the contextof treatment of blood vessels such as the coronary arteries, theinvention may also be used in any other body passageways where it isdeemed useful such as but not limited to peripheral arteries, carotidarteries, renal arteries, and/or venous applications. Furthermore, thereis no intention to be bound by any expressed or implied theory presentedin the preceding technical field, background, brief summary or thedetailed description.

Further Examples

The following examples are illustrative of several embodiments of thepresent technology:

1. A catheter comprising:an elongate shaft including a proximal portion and a distal portionextending from the proximal portion to a distal opening at a distal endof the shaft, the elongate shaft having a shaft wall, the shaft wallhaving an outer and inner surface, the shaft wall inner surface defininga guidewire lumen; anda pressure sensor having a first end coupled to the shaft wall outersurface at the distal end of the elongate shaft, the pressure sensorhaving a second end not coupled to the elongate shaft, wherein thesecond end of the pressure sensor is spaced apart from the shaft wallouter surface, such that at least a portion of the pressure sensor isisolated from the bending stresses of the shaft wall when the elongateshaft is tracked to a treatment site within a vasculature.2. The catheter of claim 1, wherein the sensor is disposed within apocket on the distal end of the elongate shaft, the pocket defined bythe shaft wall outer surface and at least one sidewall extendingsubstantially perpendicular to the shaft wall.3. The catheter of claim 2, wherein the pocket is exposed to theenvironment such that at least a portion of the sensor will besurrounded on all sides by a fluid when the elongate shaft is trackedwithin the vasculature.4. The catheter of claim 2 or 3, wherein the second end of the sensor isspaced apart from the at least one sidewall.5. The catheter of any of the preceding claims, further comprising aninterposer disposed between the shaft wall and the first end of thesensor such that the interposer elevates the sensor above the shaft wallto create a void between the shaft wall and the sensor.6. The catheter of any of the preceding claims, wherein a step is formedin the shaft wall adjacent the first end of the sensor such that thestep elevates the sensor above the shaft wall to create a void betweenthe shaft wall and the sensor.7. The catheter of any of the preceding claims, wherein the sensorcomprises a support portion adjacent the first end of the sensor, and anelongate portion, wherein the support portion is sized such that thesupport portion elevates the elongate portion of the sensor above theshaft wall to create a void between the shaft wall and the sensor. Thecatheter of any of the preceding claims, wherein a layer of adhesive isdisposed between the shaft wall and the first end of the sensor suchthat the layer of adhesive elevates the sensor above the shaft wall tocreate a void between the shaft wall and the sensor.9. A catheter comprising:an elongate shaft including a proximal portion and a distal portionextending from the proximal portion to a distal opening at a distal endof the shaft, the elongate shaft having a shaft wall, the shaft wallhaving an outer and inner surface, the shaft wall inner surface defininga guidewire lumen;an interposer having a first and second surface, wherein the interposeris mounted to the shaft wall outer surface on the interposer secondsurface; anda pressure sensor having a first end coupled to the first surface of theinterposer, wherein the second end of the pressure sensor is not coupledto the interposer or the shaft wall, the second end is spaced apart fromthe shaft wall outer surface, such that at least a portion of thepressure sensor is isolated from the bending stresses of the shaft wallwhen the elongate shaft is tracked to a treatment site within avasculature.10. The catheter of claim 9, wherein the shaft wall further defines apressure sensor wire lumen, the interposer having communication wirescoupled to the first surface wherein the communication wires extendproximally through the pressure sensor wire lumen, further whereinpressure sensor wires extend from the first surface of the interposer tothe second end of the pressure sensor.11. The catheter of claim 9 or 10, wherein the sensor and interposer aredisposed within a pocket on the distal end of the elongate shaft, thepocket defined by the shaft wall outer surface and at least one sidewallextending substantially perpendicular to the shaft wall.12. The catheter of claim 11, wherein the pocket is exposed to theenvironment such that at least a portion of the sensor will besurrounded on all sides by a fluid when the elongate shaft is trackedwithin the vasculature.13. The catheter of claim 11 or 12, wherein the second end of the sensoris spaced apart from the at least one sidewall.14. The catheter of any of claims 9 to 13, further comprising a layer ofadhesive disposed between at least one of the pressure sensor, theinterposer, and the shaft wall outer surface, such that the at least onelayer further elevates the sensor above the shaft wall to create a voidbetween the shaft wall and the sensor.15. A catheter comprising:an elongate shaft including a proximal portion and a distal portionextending from the proximal portion to a distal opening at a distal endof the shaft, the elongate shaft having a shaft wall, the shaft wallhaving an outer and inner surface, the shaft wall inner surface defininga guidewire lumen; anda pressure sensor having a support portion and an elongate portion, thesupport portion coupled to the shaft wall outer surface at the distalend of the elongate shaft, wherein the elongate portion of the pressuresensor is spaced apart from the shaft wall outer surface, such that atleast a portion of the pressure sensor is isolated from the bendingstresses of the shaft wall when the elongate shaft is tracked to atreatment site within a vasculature.16. The catheter of claim 15, wherein the sensor is disposed within apocket on the distal end of the elongate shaft, the pocket defined bythe shaft wall outer surface and at least one sidewall extendingsubstantially perpendicular to the shaft wall.17. The catheter of claim 16, wherein the pocket is exposed to theenvironment such that at least a portion of the sensor will besurrounded on all sides by a fluid when the elongate shaft is trackedwithin the vasculature.18. The catheter of claim 16 or 17, wherein the elongate portion of thesensor is spaced apart from the at least one sidewall.19. The catheter of any of claims 15 to 18, further comprising a layerof adhesive disposed between the support portion and the shaft wallouter surface such that the at least one layer of adhesive furtherelevates the sensor above the shaft wall to create a void between theshaft wall and the sensor.

While various embodiments according to the present invention have beendescribed above, it should be understood that they have been presentedby way of illustration and example only, and not limitation. It will beapparent to persons skilled in the relevant art that various changes inform and detail can be made therein without departing from the scope ofthe invention. Thus, the breadth and scope of the present inventionshould not be limited by any of the above-described exemplaryembodiments. It will also be understood that each feature of eachembodiment discussed herein, and of each reference cited herein, can beused in combination with the features of any other embodiment.

What is claimed is:
 1. A catheter comprising: an elongate shaftincluding a proximal portion and a distal portion extending from theproximal portion to a distal opening at a distal end of the shaft, theelongate shaft having a shaft wall, the shaft wall having an outer andinner surface, the shaft wall inner surface defining a guidewire lumen;and a pressure sensor having a first end coupled to the shaft wall outersurface at the distal end of the elongate shaft, the pressure sensorhaving a second end not coupled to the elongate shaft, wherein thesecond end of the pressure sensor is spaced apart from the shaft wallouter surface, such that at least a portion of the pressure sensor isisolated from the bending stresses of the shaft wall when the elongateshaft is tracked to a treatment site within a vasculature.
 2. Thecatheter of claim 1, wherein the sensor is disposed within a pocket onthe distal end of the elongate shaft, the pocket defined by the shaftwall outer surface and at least one sidewall extending substantiallyperpendicular to the shaft wall.
 3. The catheter of claim 2, wherein thepocket is exposed to the environment such that at least a portion of thesensor will be surrounded on all sides by a fluid when the elongateshaft is tracked within the vasculature.
 4. The catheter of claim 2,wherein the second end of the sensor is spaced apart from the at leastone sidewall.
 5. The catheter of claim 1, further comprising aninterposer disposed between the shaft wall and the first end of thesensor such that the interposer elevates the sensor above the shaft wallto create a void between the shaft wall and the sensor.
 6. The catheterof claim 1, wherein a step is formed in the shaft wall adjacent thefirst end of the sensor such that the step elevates the sensor above theshaft wall to create a void between the shaft wall and the sensor. 7.The catheter of claim 1, wherein the sensor comprises a support portionadjacent the first end of the sensor, and an elongate portion, whereinthe support portion is sized such that the support portion elevates theelongate portion of the sensor above the shaft wall to create a voidbetween the shaft wall and the sensor.
 8. The catheter of claim 1,wherein a layer of adhesive is disposed between the shaft wall and thefirst end of the sensor such that the layer of adhesive elevates thesensor above the shaft wall to create a void between the shaft wall andthe sensor.
 9. A catheter comprising: an elongate shaft including aproximal portion and a distal portion extending from the proximalportion to a distal opening at a distal end of the shaft, the elongateshaft having a shaft wall, the shaft wall having an outer and innersurface, the shaft wall inner surface defining a guidewire lumen; aninterposer having a first and second surface, wherein the interposer ismounted to the shaft wall outer surface on the interposer secondsurface; and a pressure sensor having a first end coupled to the firstsurface of the interposer, wherein the second end of the pressure sensoris not coupled to the interposer or the shaft wall, the second end isspaced apart from the shaft wall outer surface, such that at least aportion of the pressure sensor is isolated from the bending stresses ofthe shaft wall when the elongate shaft is tracked to a treatment sitewithin a vasculature.
 10. The catheter of claim 9, wherein the shaftwall further defines a pressure sensor wire lumen, the interposer havingcommunication wires coupled to the first surface wherein thecommunication wires extend proximally through the pressure sensor wirelumen, further wherein pressure sensor wires extend from the firstsurface of the interposer to the second end of the pressure sensor. 11.The catheter of claim 9, wherein the sensor and interposer are disposedwithin a pocket on the distal end of the elongate shaft, the pocketdefined by the shaft wall outer surface and at least one sidewallextending substantially perpendicular to the shaft wall.
 12. Thecatheter of claim 11, wherein the pocket is exposed to the environmentsuch that at least a portion of the sensor will be surrounded on allsides by a fluid when the elongate shaft is tracked within thevasculature.
 13. The catheter of claim 11, wherein the second end of thesensor is spaced apart from the at least one sidewall.
 14. The catheterof claim 9, further comprising a layer of adhesive disposed between atleast one of the pressure sensor, the interposer, and the shaft wallouter surface, such that the at least one layer further elevates thesensor above the shaft wall to create a void between the shaft wall andthe sensor.
 15. A catheter comprising: an elongate shaft including aproximal portion and a distal portion extending from the proximalportion to a distal opening at a distal end of the shaft, the elongateshaft having a shaft wall, the shaft wall having an outer and innersurface, the shaft wall inner surface defining a guidewire lumen; and apressure sensor having a support portion and an elongate portion, thesupport portion coupled to the shaft wall outer surface at the distalend of the elongate shaft, wherein the elongate portion of the pressuresensor is spaced apart from the shaft wall outer surface, such that atleast a portion of the pressure sensor is isolated from the bendingstresses of the shaft wall when the elongate shaft is tracked to atreatment site within a vasculature.
 16. The catheter of claim 15,wherein the sensor is disposed within a pocket on the distal end of theelongate shaft, the pocket defined by the shaft wall outer surface andat least one sidewall extending substantially perpendicular to the shaftwall.
 17. The catheter of claim 16, wherein the pocket is exposed to theenvironment such that at least a portion of the sensor will besurrounded on all sides by a fluid when the elongate shaft is trackedwithin the vasculature.
 18. The catheter of claim 16, wherein theelongate portion of the sensor is spaced apart from the at least onesidewall.
 19. The catheter of claim 15, further comprising a layer ofadhesive disposed between the support portion and the shaft wall outersurface such that the at least one layer of adhesive further elevatesthe sensor above the shaft wall to create a void between the shaft walland the sensor.